bug#23377: 25.0.93; Completion is extremely slow for insert-char

[Drew Adams]

> Well there's always C-x C-+ C-+ C-+ C-+. (I need to increase the size
> four times in my set up to be able to make out what the numbers are.

(You must first select window *Completions*, unless you
use Icicles.  You can't just use those keys from the
minibuffer to scale *Completions*.)

FWIW, a useful Icicles feature in this context is that
*Completions*, if in a separate frame (e.g., dedicated),
uses the same font as the window that was selected when
*Completions* was displayed.  E.g., if that window uses
a font tailored to a specific locale or set of Unicode
chars *Completions* shows candidates in that font.